Method for controlling inverter

ABSTRACT

The present invention relates to a method for controlling an inverter to prevent an unnecessary fan trip. The method includes: receiving a fan current; when the fan current is above a high trip level or is below a low trip level, incrementing an error count; when the error count reaches an error count maximum value, incrementing a trip count and initializing the error count; and when the trip count reaches a trip count maximum value, generating a fan trip signal.

CROSS-REFERENCE TO RELATED APPLICATION

Pursuant to 35 U.S.C. § 119(a), this application claims the benefit ofearlier filing date and right of priority to Korean Application No.10-2018-0052889, filed on May 9, 2018, which is herein expresslyincorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a method for controlling an inverter.

BACKGROUND

Generally, an inverter is an inverse conversion device that electricallyconverts DC to AC. An inverter used in the industry is defined as aseries of devices that control the motor speed to be used with highefficiency by receiving the power supplied from the commercial powersupply and varying the voltage and frequency by itself and supplying thevaried power to the motor. Such inverter is used in various formsthroughout the industrial field including fans, pumps, elevators,transport devices, and production lines.

Inverters include heat emission elements such as high-frequencyswitching elements such as insulated gate bipolar transistors (IGBTs),or metal oxide semi-conductor field effect transistors MOSFETs, andhigh-capacity capacitors. A cooling device, such as the fan for coolingthe exothermic component is essential to ensure the life of the inverterand provide reliability.

When a problem occurs with this cooling device, an inverter controllerdetects the failure of the cooling device. When a trip occurs, thecontroller may stop of supply of a pulse width modulation to theinverter and stops the inverter operation. However, since the operationof the inverter stops due to the detection of the failure of the coolingdevice in an inappropriate state, the reliability of the inverter systemis deteriorated.

SUMMARY

In order to solve the problem, a purpose of the present disclosure is toprovide an inverter-controlling method which improves the reliability ofan inverter by preventing an unnecessary fan trip from occurring in aninstantaneous fan overload situation.

The purpose of the present disclosure is not limited to theabove-mentioned purposes. Other purposes and advantages of the presentdisclosure that are not mentioned may be understood by followingdescriptions, and will be more clearly understood by embodiments of thepresent disclosure. It is to be further understood that the purposes andadvantages of the present disclosure may be realized and attained bymeans of means and combinations thereof recited in the appended claims.

In one aspect of the present disclosure, there is provided a method forcontrolling an inverter to prevent an unnecessary fan trip, the methodcomprising: receiving a fan current; when the fan current is above ahigh trip level or is below a low trip level, incrementing an errorcount; when the error count reaches an error count maximum value,incrementing a trip count and initializing the error count; and when thetrip count reaches a trip count maximum value, generating a fan tripsignal.

In one implementation, incrementing the error count includesincrementing the error count up while maintaining a none error count.

In one implementation, the method further comprises: when the fancurrent is between the low trip level and the high trip level,incrementing the none error count; and when the none error count reachesa none error count maximum value, initializing the trip count.

In one implementation, incrementing the none error count includesincrementing the none error count while maintaining the error count.

In one implementation, initializing the trip count includes initializingboth the error count and the none error count.

In one implementation, the method further comprises: receivingtemperature information about a temperature in the inverter; when thetemperature in the inverter is higher than or equal to a firsttemperature, incrementing the trip count; and when the trip countexceeds a first maximum value, generating a fan trip signal.

In one implementation, the method further comprises: when thetemperature in the inverter is lower than the first temperature and ishigher than or equal to a second temperature lower than the firsttemperature, incrementing the trip count; and when the trip countexceeds a second maximum value greater than the first maximum value,generating a fan trip signal.

According to the present disclosure, when the fan current drifts out ofthe normal range at a beginning of operation of the fan but operateswithin the normal range after a certain period of time from thebeginning, the fan trip signal is not generated rapidly, such that thereliability of the inverter can be improved.

In addition, the present disclosure may improve the reliability of theinverter by determining whether to generate the trip signal inconsideration of not only the fan current but also the invertertemperature information. Thus, the customer satisfaction can beimproved.

Further specific effects of the present disclosure as well as theeffects as described above will be described in conduction withillustrations of specific details for carrying out the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration of a conventional inverter system.

FIG. 2 is a flow chart for describing an operation of a controller inthe conventional inverter system as shown in FIG. 1.

FIG. 3 is an example diagram for describing fan current and fan tripsignal generation.

FIG. 4 is a configuration diagram of an inverter system to which oneembodiment of the present disclosure is applied.

FIG. 5 is a flow chart describing an operation of one embodiment of acontroller in the inverter system in accordance with the presentdisclosure.

FIG. 6 and FIG. 7 are example diagrams for describing the operation ofthe controller according to FIG. 5.

FIG. 8 is a flow chart describing an operation of another embodiment ofa controller in the inverter system in accordance with the presentdisclosure.

DETAILED DESCRIPTION

Hereinafter, a method for controlling an inverter in accordance with thepresent disclosure will be described with reference to the accompanyingdrawings.

For simplicity and clarity of illustration, elements in the figures. arenot necessarily drawn to scale. The same reference numbers in differentfigures. denote the same or similar elements, and as such performsimilar functionality. Also, descriptions and details of well-knownsteps and elements are omitted for simplicity of the description.Furthermore, in the following detailed description of the presentdisclosure, numerous specific details are set forth in order to providea thorough understanding of the present disclosure. However, it will beunderstood that the present disclosure may be practiced without thesespecific details. In other instances, well-known methods, procedures,components, and circuits have not been described in detail so as not tounnecessarily obscure aspects of the present disclosure.

The above objects, features and advantages will become apparent from thedetailed description with reference to the accompanying drawings.Embodiments are described in sufficient detail to enable those skilledin the art in the art to easily practice the technical idea of thepresent disclosure. Detailed descriptions of well-known functions orconfigurations may be omitted in order not to unnecessarily obscure thegist of the present disclosure. Hereinafter, embodiments of the presentdisclosure will be described in detail with reference to theaccompanying drawings. Throughout the drawings, like reference numeralsrefer to like elements.

Unless defined otherwise, all terms used herein have the same meaning ascommonly understood by one of ordinary skill in the art. When the termsused herein are in conflict with a general meaning of the term, themeaning of the term is in accordance with a definition used herein.

Examples of various embodiments are illustrated and described furtherbelow. It will be understood that the description herein is not intendedto limit the claims to the specific embodiments described. On thecontrary, it is intended to cover alternatives, modifications, andequivalents as may be included within the spirit and scope of thepresent disclosure as defined by the appended claims.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a” and “an” are intendedto include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising”, “includes”, and “including” when used in thisspecification, specify the presence of the stated features, integers,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers,operations, elements, components, and/or portions thereof. As usedherein, the term “and/or” includes any and all combinations of one ormore of the associated listed items. Expression such as “at least oneof” when preceding a list of elements may modify the entire list ofelements and may not modify the individual elements of the list.

It will be understood that, although the terms “first”, “second”,“third”, and so on may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondescribed below could be termed a second element, component, region,layer or section, without departing from the spirit and scope of thepresent disclosure.

In addition, it will also be understood that when a first element orlayer is referred to as being present “on” a second element or layer,the first element may be disposed directly on the second element or maybe disposed indirectly on the second element with a third element orlayer being disposed between the first and second elements or layers. Itwill be understood that when an element or layer is referred to as being“connected to”, or “coupled to” another element or layer, it can bedirectly on, connected to, or coupled to the other element or layer, orone or more intervening elements or layers may be present. In addition,it will also be understood that when an element or layer is referred toas being “between” two elements or layers, it can be the only element orlayer between the two elements or layers, or one or more interveningelements or layers may also be present.

Hereinafter, a conventional inverter-controlling method will bedescribed with reference to FIGS. 1 to 3. An inverter-controlling methodin accordance with one embodiment of the present disclosure will bedescribed with reference to FIGS. 4 to 8.

FIG. 1 shows a configuration of a conventional inverter system.

When an AC power is supplied from a power unit 200, a rectifying module110 of an inverter 100 rectifies the AC power to a DC power. Thus, a DClink capacitor 120 is charged with the DC link voltage. A controller 400provides a pulse width modulation (PMW) signal to the inverting module140. The inverting module 140 converts the DC link voltage to an ACvoltage via the PWM signal and outputs the converted AC voltage to amotor 300.

A switched mode power supply (SMPS) 130 starts to operate, via the DClink voltage, and, a fan voltage V_FAN for operating a cooling device isprovided from the SMPS 130 to the cooling device 500. The fan 510 of thecooling device 500 receives the fan voltage V_FAN and starts itsoperation. A fan controller 520 detects a fan current I_FAN andtransfers the detected current to the controller 400. When a failurecondition of the fan 510 occurs, the controller 400 outputs a fan tripsignal FAN_Trip to stop the operation of the inverter 100.

FIG. 2 is a flow chart for describing an operation of the controller inthe conventional inverter system as shown in FIG. 1. FIG. 3 is anexample diagram for describing fan current and fan trip signalgeneration.

A level of the fan current at which a trip occur when the fan current ismaintained above a certain level by setting is referred to as a ‘hightrip level’ of the fan current. A level of the fan current at which atrip occurs when the fan current is maintained below a certain level isreferred to as a ‘low trip level’ of the fan current. Those are shown inFIG. 3.

Referring to FIG. 2, the controller 400 receives the fan currentdetected by the fan controller 520 S21 and determines whether the fancurrent exceeds the high trip level or is lower than the low trip levelS22. If so, the controller 400 increases an error count S23.

Then, when the error count is equal to or greater than a maximum valueS24, the controller 400 generates a fan trip signal S25. When the fantrip signal occurs, the supply of the PWM signal to the inverter module140 stops, thereby stopping the operation of the inverter 100.

The reason why the fan trip signal is generated in this manner is toprevent the inverter 100 from overheating. When the fan trip signal isgenerated, the power supply to the inverter 100 is not cut off. Anoperation of the motor 300 stops.

However, since the conventional fan control method as described abovedetermines the trip using only the fan current. Thus, in a case wherethe inverter 100 is initially operated after being left at a lowtemperature for a long time, the fan 510 operates normally but the fancurrent intermittently rises due to an increase in a frictional force ofthe blade of the fan 510, resulting in the fan trip. Alternatively, whendusts or the like instantaneously flows into the fan 510 and thus thefan current suddenly rises, there is a problem that the fan trip mayoccur although a temperature of the inverter 100 itself does not rise.

When the fan trip occurs due to factors other than the temperatureincrease of the inverter 100 itself, the operation of the inverter 100is stopped and the operation of the motor 300 is stopped. Thus, the taskthat the user is being involved is forcibly stopped, resulting in atemporal and economical loss. This leads to a problem that thereliability of the product is lowered.

Therefore, it is necessary to generate the trip only when thetemperature of the inverter 100 rises excessively due to a fault in theinverter 100.

The present disclosure is intended to solve such a problem and thusprovides an inverter cooling device-controlling method which improvesthe reliability of the inverter by preventing the occurrence of anunnecessary fan trip in a momentary fan overload situation.

FIG. 4 is a configuration diagram of an inverter system to which oneembodiment of the present disclosure is applied.

As shown in FIG. 4, the system to which the present disclosure isapplied includes an inverter 1 for converting an AC voltage applied fromthe power unit 2 into a voltage having a predetermined magnitude and afrequency, and providing the converted voltage to the motor 3; acontroller 4 which provides a pulse width modulation PWM signal and atrip signal to the inverter 1, and a cooling device 5 for cooling theinverter 1.

The inverter 1 includes a rectifying module 11 for converting an ACvoltage input from the power unit 2 into a DC voltage, a DC linkcapacitor 12 for storing the DC voltage from the rectifying module 11, aDC power supply 13 for supplying the DC voltage stored in the DC linkcapacitor 12 to the cooling device 5 as a power source, an invertingmodule 14 composed of semiconductor switching elements such insulatedgate bipolar mode transistors (IGBTs) wherein the inverting module 14uses the PWM signal from the controller 4 to convert the DC link voltageinto an AC voltage and outputs the AC voltage to the motor, and atemperature detection module 15 for detecting a temperature of theinverting module 14.

The DC power supply 13 may be, but is not limited to, a switched modepower supply SMPS. Various types of power supply devices may be usedthat provide the DC link voltage stored in the DC link capacitor 12 as apower source to other components.

The temperature detection module 15 is disposed inside the invertingmodule 14 because an element that generates most of the heat in theinverter 1 is the switching elements of the inverting module 14.However, the present disclosure may not be limited thereto. Thetemperature detection module 15 may be disposed at various positionswhere the internal temperature of the inverter 1 may be appropriatelymeasured. The temperature detection module 15 may be, for example, anNCT (Negative Temperature Coefficient of Resistance) temperature sensor.Temperature information NTC about a temperature inside the inverter 1detected by the temperature detection module 15 may be transmitted tothe controller 4.

The cooling device 5 may include a fan 51 and a fan controller 52.However, in one embodiment of the present disclosure, the fan 51 is usedas an example of the cooling device 5, but is not limited thereto. Thepresent disclosure does not exclude the use of various types of coolingdevices.

When the DC link capacitor 12 is charged with the DC link voltage, thisallows the DC power supply 13 to start operating. The DC power supply 13provides the fan voltage V_FAN for operating the cooling device 5 to thefan controller 52 of the cooling device 5. The fan 51 may be suppliedwith the fan voltage V_FAN from the fan controller 52 and may start theoperation of the fan. The fan controller 2 may detect the fan currentI_FAN of the fan 51 and provide the detected fan current to thecontroller 4.

The controller 4 may generate a fan trip based on the fan current I_FANreceived from the fan controller 52 and/or the temperature informationNCT about the inverter as detected by the temperature detection module.FIG. 5 is a flow chart for describing an example operation of thecontroller in the inverter system of the present disclosure. FIG. 5shows the operation of determining whether to generate the fan tripbased on the fan current. FIG. 6 and FIG. 7 are example diagrams fordescribing the operation of the controller according to FIG. 5. FIG. 6shows a case where no trip occurs, and FIG. 7 shows a case where tripoccurs.

Further, FIG. 8 is a flow chart describing an operation of anotherembodiment of a controller in the inverter system of the presentdisclosure. FIG. 8 illustrates a determination of whether to generatethe fan trip based on the inverter temperature information.

In one embodiment of the present disclosure, the controller determineswhether to generate the fan trip primarily based on the fan current, andthen determines whether to generate the fan trip secondarily based onthe temperature information. Alternatively, the controller 4 maydetermine whether to generate the fan trip only based on the fancurrent. Alternatively, the controller 4 may determine whether togenerate the fan trip only based on the temperature information.

Referring to FIG. 5, in one embodiment of the present disclosure, thecontroller 4 may receive a fan current from the fan controller 52 S51.When the fan current exceeds the high trip level or is below the lowtrip level S52, the controller 4 may increase an error count andmaintain a none error count S53.

The increase in the error count lasts until the error count reaches amaximum value MAX. When the error count reaches the error count maximumvalue MAX, the controller may increase the trip count and initialize theerror count at S55. This operation S55 continues until the trip countreaches a maximum value. When the trip count reaches the trip countmaximum value MAX S56, the controller 4 may generate a fan trip signaland stop the inverter operation.

In one example, when the fan current is in the normal range between thelow trip level and the high trip level, the controller 4 increases thenone error count and maintains the error count S58. This operation S58continues until the none error count reaches the maximum value MAX. Whenthe none error count reaches the maximum value MAX S59, the controllermay initialize the trip count, error count and none error count. Thetrip count, error count, and none error count are initialized when thenone error count reaches the maximum value MAX because the controller 4has determined that the fan normally operates and that there will occurno trip due to the fan current again. This will be described using FIG.6 and FIG. 7 as follows. FIG. 6 shows a case where no trip occurs, andFIG. 7 shows a case where trip occurs.

Referring to FIG. 6, it may be seen that the fan current is going backand forth between the high trip level and the low trip level, and, then,the fan current has entered the normal range. In this case,conventionally, when the error count reaches the maximum value, a tripoccurs immediately.

According to one embodiment of the present disclosure, when the fancurrent is greater than the high trip level, the error count continuesto increase and 6A, while the none error count remains constant. Then,when the fan current enters the normal range (a range of values higherthan the low trip level and lower than the high trip level), the errorcount is maintained 6C, and the none error count is increased 6D.Thereafter, when the fan current goes out of the normal range, the errorcount increases. Then, when the error count reaches the error countmaximum value MAX, the controller may increase the trip count 6E andinitialize the error count.

This process is repeated and thus the fan current as output is stable inthe normal range. In this case, the none error count continuouslyincreases 6G. Then, when the none error count reaches the maximum valueMAX, the trip count is initialized, and the error count and none errorcount are initialized. As mentioned above, the trip count, error count,and none error count are initialized when the none error count reachesthe maximum value MAX because the controller 4 has determined that thefan normally operates.

Thus, according to one embodiment of the present disclosure, thecontroller does not generate the fan trip signal rapidly even when thefan current is outside the normal range at the beginning of operation,but the fan operates within the normal range after a certain period oftime from the beginning, thereby improving the reliability of theinverter. Referring to FIG. 7, unlike the case of FIG. 6, the fancurrent continues to repeatedly switch into between the normal range andthe abnormal range such that the fan current is not maintained in thenormal range.

According to one embodiment of the present disclosure, when the fancurrent is greater than the high trip level, the error count continuesto increase, while the none error count is kept constant. Then, when thefan current enters the normal range (a range of values higher than thelow trip level and lower than the high trip level), the error count ismaintained, while the none error count is incremented. Thereafter, whenthe fan current goes out of the normal range, the error count increases.When the error count reaches the maximum value MAX, the controller mayincrease the trip count and initialize the error count. This isdescribed above with reference to FIG. 6.

In FIG. 7, when the error count reaches the maximum value MAX 3 timeswhile the trip count increases 3 times, the trip count reaches themaximum value MAX, thereby to cause a trip 7A. In one embodiment of thepresent disclosure, an example where the error count and the none errorcount are maintained or increased according to the fan current even whenthe trip occurs is illustrated. The present disclosure is not limitedthereto. Alternatively, when the trip occurs, both the error count andthe none error count may be initialized.

In one embodiment of the present disclosure, an example where the tripoccurs when the error count reaches the maximum value MAX three times(the trip count maximum value MAX is 3) is illustrate. The presentdisclosure is not limited thereto. The trip count MAX may vary dependingon the sensitivity of the system.

According to one embodiment of the present disclosure, the controllermay use both the inverter temperature information and the fan current todetermine whether to generate the fan trip. That is, the controllerprimarily uses the fan current to determine whether to generate the fantrip. Then, the controller secondarily uses the inverter temperatureinformation to determine whether to generate the fan trip.Alternatively, the controller may use either the fan current ortemperature information to determine whether to generate the fan trip.FIG. 8 illustrates how to determine whether to generate the fan tripusing the inverter temperature information.

Referring to FIG. 8, the controller 4 may receive the temperatureinformation of the inverter 1 from the temperature detection module 15S81. Thus, when the temperature does not exceed a set first temperatureS82, the controller may also determine whether a certain duration haselapsed since the inverter 1 was powered on S83. When the certainduration has not elapsed since the inverter 1 was powered on, thecontroller determines this period as an inverter drive transitionperiod. In this connection, the controller is configured to determinewhether to cause the fan trip only if the certain duration has elapsed.The certain duration may be, for example, 180 seconds, but is notlimited to this. The certain duration may vary depending on how long thetransition period is maintained after the inverter 1 is powered on.Further, the set first temperature may be, for example, 10 degrees C.However, it should be understood that the present disclosure is notlimited thereto and the first temperature has various values.

When the temperature of the inverter 1 exceeds the first temperature atS82, or when the temperature does not exceed the first temperature at82, the controller may determine whether the temperature of the inverter1 is above or equal to a second temperature S84 if the certain durationhas elapsed since the power was applied to the inverter 1. In thisconnection, the second temperature may be, for example, 40° C., but thepresent disclosure is not limited thereto. The control temperature mayvary depending on the environment in which the inverter 1 is used.

When the temperature of the inverter 1 is equal to or higher than thesecond temperature, the controller 4 may increase the trip count S85.When the trip count exceeds a first maximum value MAX1 S86, thecontroller may generate a fan trip signal S87.

Alternatively, when the temperature of inverter 1 is below the secondtemperature, the controller 4 may also increase the trip count S88.Further, when the trip count exceeds a second maximum value MAX S89, thecontroller may generate a fan trip signal S89.

In one embodiment of the present disclosure, for example, the firstmaximum value MAX1 of the trip count may be 3. The second maximum valueMAX2 of the trip count may be 10. That is, when the temperature of theinverter 1 is higher than or equal to the second temperature 40° C., thetrip count maximum value MAX is set to a small number. This indicates anenvironment in which the inverter 1 may have a great risk if thetemperature is higher than or equal to the second temperature. On theother hand, a maximum value MAX applied when the temperature of theinverter 1 is lower than the second temperature 40° C. may be differentfrom that applied when the temperature of the inverter 1 is higher thanor equal to the second temperature 40° C. This indicates an environmentin which the inverter 1 may have a great risk, thereby to prevent anunnecessary trip.

Thus, according to one embodiment of the present disclosure, thecontroller may consider the inverter temperature as well as the fancurrent whether to generate the trip signal. This may improve thereliability of the inverter.

It will be apparent to those skilled in the art that variousmodifications and variations may be made in the present inventionwithout departing from the spirit of the present disclosure. Thetechnical scope of the present disclosure is not limited to the contentsdescribed in the embodiments but should be determined by the claims andequivalents thereof

What is claimed is:
 1. A method for controlling an inverter to preventan unnecessary fan trip, the method comprising: receiving a fan current;when the fan current is above a high trip level or is below a low triplevel, incrementing an error count; when the error count reaches anerror count maximum value, incrementing a trip count and initializingthe error count; and when the trip count reaches a trip count maximumvalue, generating a fan trip signal.
 2. The method of claim 1, whereinincrementing the error count includes incrementing the error count upwhile maintaining a none error count.
 3. The method of claim 1, whereinthe method further comprises: when the fan current is between the lowtrip level and the high trip level, incrementing the none error count;and when the none error count reaches a none error count maximum value,initializing the trip count.
 4. The method of claim 3, whereinincrementing the none error count includes incrementing the none errorcount while maintaining the error count.
 5. The method of claim 3,wherein initializing the trip count includes initializing both the errorcount and the none error count.
 6. The method of claim 1, wherein themethod further comprises: receiving temperature information about atemperature in the inverter; when the temperature in the inverter ishigher than or equal to a first temperature, incrementing the tripcount; and when the trip count exceeds a first maximum value, generatinga fan trip signal.
 7. The method of claim 6, wherein the method furthercomprises: when the temperature in the inverter is lower than the firsttemperature and is higher than or equal to a second temperature lowerthan the first temperature, incrementing the trip count; and when thetrip count exceeds a second maximum value greater than the first maximumvalue S89, generating a fan trip signal.